1. Field of the Invention
The present invention relates to an error counting apparatus and method for counting the error number of pre-pit signals in the recording area containing the emboss portion formed on the optical disc.
2. Description of the Related Art
In the prior art, the DVD-RW (Digital Versatile Disc-ReWritable) is known as an example of the optical disc. In this DVD-RW disc, the lead-in area is provided prior to the data area. The control data zone is provided in this lead-in area. This control data zone is constructed by 192 ECC (Error Correction Code) blocks that consist of 176 control data blocks and 16 servo blocks. In this control data block, the control data are recorded by the deep emboss pits (readable embosses), and such control data cannot be rewritten but can be read. In the servo block, the shallow emboss pits (unreadable embosses) are recorded so as to make the reading of the land pre-pit possible in the situation that the rewrite of the control data is inhibited, as described later. In this case, please see the description of patent application Ser. No. 2000-78102 filed on Mar. 21, 2000 by the applicant of this application to know the details.
Meanwhile, the land pre-pit (LPP) signal indicating the address, etc. on the disc is recorded on the land track. In this case, the land pre-pit signal is not recorded on the land tracks, which correspond to the above 176 control data blocks, because such land pre-pit signal prevents the reading of the control data whereas the land pre-pit signal is recorded on the land tracks, which correspond to the above 16 servo blocks, to acquire the address of the subsequent data area.
By the way, it is stipulated in the DVD-RW format to satisfy the error rate of less than 3% in detecting the land pre-pit signal in the 16 servo blocks. Therefore, the disc manufacturer has to measure the error rate in this unreadable emboss portion. In the prior art, it is decided whether or not the disc can satisfy such standard, by supplying the pre-pit error pulse signal (indicating the error number) and the ECC block pulse signal (indicating the block number), which are output from the pre-pit signal decoder, to the dedicated counters respectively, then reading simply the counted values of respective counters with the eye, and then calculating the error rate.
However, since not only the unreadable emboss portion is constructed by the 16 ECC blocks (servo blocks) and is very short in length but also the land pre-pit signal is not recorded on the preceding readable emboss portion, the pre-pit error pulse signal is always output from the pre-pit signal decoder during the period when the readable emboss portion is reproduced. Therefore, it is very difficult to count precisely the error number from the beginning of the unreadable emboss portion. Also, it is possible to detect the error by monitoring the RF signal as the reproduced output with the eye via the oscilloscope, etc. However, it is difficult to execute such monitoring in the disc manufacturing step since the high skill is required for such monitoring.